Siemens LMV50 Series Manual page 228

O2 trim control
(only with LMV52
system)
General
228/327
Building Technologies
The O2 trim control system of the LMV52 offers a number of operating modes. In
operating mode conAutoDeac, O2 trim control is automatically deactivated by the
LMV52 if the O2 alarm responds, or if a fault in connection with actual value acquisition
of O2 occurs (QGO20, PLL52, O2 sensor test, etc.). Also, O2 trim control can be
deactivated manually by selecting mandeact. For this reason, the ratio control curves
with the LMV52 must always be set such that there are sufficient amounts of excess
air, irrespective of environmental conditions (e.g. combustion chamber and fuel
pressure, and temperature and pressure of the combustion air) across the entire load
range – same as with a system without O2 trim control (LMV50/LMV51). Also, the ratio
control curves must be proven. The actual O2 value should not fall below the O2
setpoint of O2 trim control.
A sufficient number of curvepoints (for actuator positions, O2 setpoints, etc.) should be
stored to ensure that there is a linear progression of the O2 value across the entire load
range. The second curvepoint must correspond to the low-fire position (or be set to a
lower value). The first curvepoint must lie sufficiently below curvepoint 2 (at about 50 %
load) so that the curves are defined for reducing the air rate by O2 trim control below
the low-fire position also.
The O2 min. value represents the switch-off threshold of the O2 alarm function and
must be set and proven such that – across the entire load range and while taking into
account the combustion chamber and fuel pressure as well as the temperature and
pressure of the combustion air – there will be no dangerous increase of the CO and/or
soot values.
On the other hand, the safety distance from the dangerous area should be selected as
small as possible to prevent inadvertent or undesired shutdowns (guide values: CO
<2000 ppm Vol % or soot number <3 according to Bacharach).
The O2 setpoint must have an adequate distance from the above mentioned O2 min.
value (guide value: O2 setpoint = O2
It must be made certain that all safety notes and the notes on mounting, electrical
installation and service according to the above mentioned chapter and Data Sheets are
complied with.
Basic Documentation LMV5...
14 Duties of the authorized inspector
+1% O2).
min. value
CC1P7550en
22.05.2018